Microprocessors are used today for performing the internal operations of modern instruments. Additionally, computers and microprocessors are used to control test and measurement systems. The primary method used for interconnecting and communicating between instruments and control computers (controllers) is the IEEE 488 bus.
The IEEE 488 bus is essentially an electrical signal transmission bus with a predefined set of lines. A set of predefined protocols govern the methodology for transferring information over the bus from a controller to specified devices, and vice versa. By using an industry standard bus, the manufacturers of a wide variety of instruments can ensure that standard software packages and interface circuits can be used to connect their instruments to microprocessor based controllers. That is, purchasers of these instruments do not need to buy a different customized controller for each instrument, because all such instruments use the same set of signal lines and the same set of communication protocols.
IEEE 488-1978, as well as the newer IEEE 488.1-1987 standard, defines a data settling time, T1, that is used by all devices (instruments and controllers) that source "multiline" messages (i.e., messages containing multiple bits transmitted parallel) onto the IEEE 488.1 bus. IEEE Standards 488-1978 and 488.1-1987 allow different values for T1, depending on the configuration of the system and on the type of data line drivers used by the device performing the source handshake. The maximum multiline data transfer rate that is compatible with these standards is 1 megabyte per second. However, advances in instrumentation are making this data transfer rate limitation a bottleneck in terms of inter-instrument communication. The inventors of the present invention believe that there is a need for an inter-instrument communication standard that can achieve higher data transfer rates. The present invention provides a backwards-compatible modification of the IEEE 488.1 bus standard that can achieve data transfer speeds of up to 8 megabytes per second.